Electrical tachometer



June 19, 1956 MOENTEE 2,751,553

ELECTRIC TACHOMETER Filed July 13, 1953 INVENTOR. H0 WARD G. MCENTEE I I E ZAHyS.

Fatented June 19, 1956 2,751,553 ELECTRICAL TACHOMETER Howard G. MeEntee, Ridgewood, N. J. Application July 13, 1953, Serial No. 367,663 3 Claims. (Cl. 324-70) This invention relates to an electrical tachometer.

An object of this invention is to provide a simple and inexpensive electrical tachometer which can be connected to the ignition system of an internal combustion engine and which does not interfere with the normal operation of the ignition system.

A further object of this invention is to provide an instrument which indicates whether the ignition system is operating properly or not, and which also detects improper operation of the breaker points of the engine ignition system or point bounce.

From the following detailed description, and the accompanying drawing, the above and other objects and features of the invention will be apparent to those having ordinary skill in the art to which it pertains.

The single view of the drawing is a diagrammatic illustration of an electrical tachometer constructed in accordance with an embodiment of this invention as applied to the ignition system of an internal combustion engine.

In the following detailed description, and the drawing, like reference characters indicate like parts.

In the drawing, the battery of an ignition system for an internal combustion engine is indicated at 10. The battery is connected in series with a primary winding 12 of an induction coil 13 and with breaker points 14 which are opened and closed by a cam 15 in the customary manner. A condenser 15' is connected across the breaker points as shown. The secondary or high voltage winding 16 of the induction coil is connected by a conductor 17 to a distributor 18. The points of the distributor 18 are connected to the various spark plugs 19, only one of which is shown.

The tachometer includes a transformer 21 having windings 22 and 23. Winding 22 is connected in series with a resistor 24 across points 14. Winding 23 is connected through a condenser 25 and an adjustable resistor 26 to a rectifier 27. The output of the rectifier is impressed on a meter or galvanometer 28, the reading of which is proportional to the speed of the engine. A condenser 29 and a gaseous discharge tube 30 are connected in parallel across the terminals of transformer winding 23.

The transformer 21 is a stepup transformer, that is, the output voltage of winding 23 is higher than the input voltage to winding 22. I have found that if transformer 21 has a ratio of turns in winding 22 to turns in winding 23, of about 1:15, a satisfactory operative tachometer meter circuit is provided.

The gaseous discharge tube 30 may be a neon bulb of the type known as NE-Sl and the condenser 29 may have a capacity of 0.02 microfarad. The condenser 29 serves to smooth out the pulsations produced in the primary circuit of transformer 21 while the tube 30 acts to stabilize the circuit.

In operation, tube 30 flashes once for each break of points 14. At low speeds the flashes are quite apparent but at higher speeds the flashes become a steady glow to the naked eye.

Meter 28 records the current output of rectifier 27. The value of that current at any instant is proportional to the engine speed: therefore the meter 28 can be calibrated to indicate directly the engine speed. The adjustable resistor is adjusted so that the meter 28 has a full scale reading at the highest possible engine speed.

In the drawing, leads 31 and 32, by means of which the tachometer is attached to the engine ignition system are shown connected across points 14. However, if desired, the leads may be connected directly across ignition coil primary 12.

The pointer of the meter will advance smoothly as the engine is smoothly accelerated to high speed if the breaker points are operating properly. However, should the pointer be seen to jump ahead suddenly rather than advancing smoothly and in step with the increase in engine speed, it is an indication that the points are bouncing and need attention.

The device illustrated in the drawing and disclosed above is subject to structural modification without departing from the spirit and scope of the appended claims.

Having described my invention, what I claim as new and desire to secure by Letters Patent, is:

1. An electrical tachometer for an internal combustion engine having an ignition system, there being breaker points in said ignition system, which comprises a transformer having primary and secondary windings, means for connecting the primary winding of said transformer across one of the components of the ignition system, a metering circuit comprising a condenser, a resistor connected in series with the secondary winding of the transformer, a second condenser and a gaseous discharge bulb connected in parallel across said secondary transformer winding, whereby an electric current passes through the metering circuit Whose magnitude is proportional to the rate of breaking of the breaker points, and means for measuring the current passing through the metering circuit.

2. An electrical tachometer for an internal combustion engine having an ignition system, there being breaker points in said ignition system, which comprises a transformer having primary and secondary windings, means for connecting the primary winding of said transformer across one of the components of the ignition system, a metering circuit comprising a condenser, a resistor connected in series with the secondary winding of the transformer, a second condenser and a neon tube connected in parallel across said secondary transformer winding, whereby an electric currrent passes through the metering circuit whose magnitude is proportional to the rate of breaking of the breaker points, and means for measuring the current passing through the metering circuit.

3. An electrical tachometer for an internal combustion engine having an ignition system, there being breaker points in said ignition system, which comprises a transformer having primary and secondary windings, means for connecting the primary winding of said transformer across one of the components of the ignition system, a metering circuit comprising a condenser, a resistor connected in series with the secondary winding of the transformer, a second condenser and a gaseous discharge bulb connected in parallel across said secondary transformer winding, whereby an electric current passes through the metering circuit whose magnitude is proportional to the rate of breaking of the breaker points, and current measuring means for measuring the current passing through the metering circuit, said current measuring means comprising a rectifier connected in series with the first mentioned condenser, the resistor, and the secondary winding of the transformer, and a galvanometer connected to the rectifier to measure the current passing through the metering circuit.

References Cited in the file of this patent UNITED STATES PATENTS 2,108,014 Jones Feb. 8, 1938 2,221,591 Lansdale Nov. 12, 1940 2,228,367 Sanders Jan. 14, 1941 2,335,247 Ianson Nov. 30, 1948 FOREIGN PATENTS 865,830 Germany Feb. 5, 1953 

